Passing tokens to a function

I'd like to make an XMLTABLE() function, probably in plpython (not C).
And I'd like to follow the SQL/XML standard. So a function call should
look something like this:

SELECT *
FROM XMLTABLE('//node'
   PASSING xmldoc
   COLUMNS id INT PATH '@id',
     name VARCHAR(30) PATH 'name')

Is this possible to pass in the tokens or do I need to abandon the
standard and just take parameters, probably something more like:

SELECT *
FROM XMLTABLE('//node', xmldoc,
array[xt_column('id', INT, '@id'), xt_column('name', VARCHAR(30), 'name')])